A New Approach to Earth’s Gravity Field Modeling Using GPS-Derived Kinematic Orbits and Baselines

Qile Zhao,Xiang Guo

doi:10.3390/rs11141728

Abstract

Earth’s gravity field recovery from GPS observations collected by low earth orbiting (LEO) satellites is a well-established technique, and kinematic orbits are commonly used for that purpose. Nowadays, more and more satellites are flying in close formations. The GPS-derived kinematic baselines between them can reach millimeter precision, which is more precise than the centimeter-level kinematic orbits. Thus, it has long been expected that the more precise kinematic baselines can deliver better gravity field solutions. However, this expectation has not been met yet in practice. In this study, we propose a new approach to gravity field modeling, in which kinematic orbits of the reference satellite and baseline vectors between the reference satellite and its accompanying satellite are jointly inverted. To validate the added value, data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission are used. We derive kinematic orbits and inter-satellite baselines of the twin GRACE satellites from the GPS data collected in the year of 2010. Then two sets of monthly gravity field solutions up to degree and order 60 are produced. One is derived from kinematic orbits of the twin GRACE satellites (‘orbit approach’). The other is derived from kinematic orbits of GRACE A and baseline vectors between GRACE A and B (‘baseline approach’). Analysis of observation postfit residuals shows that noise in the kinematic baselines is notably lower than the kinematic orbits by 50, 47 and 43% for the along-track, cross-track and radial components, respectively. Regarding the gravity field solutions, analysis in the spectral domain shows that noise of the gravity field solutions beyond degree 10 can be significantly reduced when the baseline approach is applied, with cumulative errors up to degree 60 being reduced by 34%, when compared to the orbit approach. In the spatial domain, the recovered mass changes with the baseline approach are more consistent with those inferred from the K-Band Ranging based solutions. Our results demonstrate that the proposed baseline approach is able to provide better gravity field solutions than the orbit approach. The findings may facilitate, among others, bridging the gap between GRACE and GRACE Follow-On satellite mission.

Highlights

Knowledge of temporal variations of the Earth’s gravity field is of importance to understand large-scale mass transport at and below the Earth’s surface
To make full use of the precise kinematic baseline vectors, we propose a new approach in this study, where kinematic orbits of the reference satellite and kinematic baseline vectors between the reference satellite and its accompanying satellite are taken as observations during gravity field recovery
It can be observed that the PSD1/2s for both kinematic orbits and baselines exhibit clear frequency-dependent behaviors, which necessitates the frequency-dependent data weighting (FDDW) scheme adopted in this study

Summary

Introduction

Knowledge of temporal variations of the Earth’s gravity field is of importance to understand large-scale mass transport at and below the Earth’s surface. It has been mostly observed with the ultra-precise K-Band ranging (KBR) measurements from the Gravity Recovery and Climate Experiment (GRACE) mission [1] and its successor, i.e., the GRACE Follow-On (GFO) mission. GPS-derived kinematic orbits are usually taken as pseudo-observations in gravity field modeling. Since GPS data are about three orders of magnitude less precise than the KBR data, they are only sensitive to temporal variations at low spherical harmonic degrees (

Results

Discussion

Conclusion